Convicted terrorist Michael McKevitt will find out this afternoon whether he will be released from prison after serving 13 years.

The alleged leader of the Real IRA claims he is entitled to an enhanced one-third remission of his 20-year sentence instead of the usual 25%.

He was jailed in August 2003 after being convicted in Dublin's Special Criminal Court of directing a terrorist organisation and of being a member of the Real IRA.

His 20-year sentence jail sentence was backdated to March 29, 2001. The High Court has been told McKevitt believes that he should have been released from Portlaoise Prison on July 26 last.

Michael O'Higgins SC told the court that McKevitt ticked all the boxes for enhanced remission.

He said that according to judgments by Mr Justice Max Barrett and Mr Justice Gerard Hogan, McKevitt ought to have been released. He said they allowed a prisoner to a one-third remission of sentence if he had been of good conduct and had engaged in authorised activities to prepare him for release.

Mr O'Higgins told the court the Justice Minister had used "irrelevant considerations" such as a garda intelligence report to refuse McKevitt full remission.

Diarmaid McGuinness SC said it would be a "manifest absurdity" if the minister were to be prohibited from taking into consideration elements other than French or advanced maths studies in order to assess if a prisoner was less likely to reoffend.

Counsel told the court the rule did not mean a prisoner automatically received a full remission and the power was granted to the minister, not to a prisoner who turned up at one or two activities.

Mr McGuinness said the rule required the minister to assess McKevitt's risk to reoffend and she had found it had not been lessened by his engagement in structured activities.